Project Summary Organic anion transporters (OATs) mediate the absorption, distribution, and excretion of a diverse array of environmental toxins, and clinically important drugs, including anti-cancer drugs, anti-viral agents, diuretics, antibiotics, anti-hypertensives, and anti-inflammatories. OATs are abundantly expressed in kidney, liver, brain, and placenta. OAT dysfunction in these organs significantly contributes to the renal, hepatic, neurological, and fetal toxicity and disease. Despite such a vital role, how and at what level and to what extents the transporters are regulated are important questions remain to be answered. In this application, we will explore two new targets, through which OAT activity can be regulated: deubiquitinases and proteasomes. Three Specific Aims are outlined. In Specific Aim I, we will identify the specific deubiquitinases that modulate distinct steps in OAT trafficking in cultured cells and in tissue slices. In Specific Aim II, we will assess the role of proteasomal inhibition in OAT-mediated drug transport in cultured cells. In Specific Aim III, we will evaluate the physiological and pathophysiological relevance of proteasomal inhibition in OAT-mediated drug transport in animals. Combined approaches of biochemistry, molecular biology, cell biology, and physiology will be employed for the proposed studies in cultured cells, in tissue slices, and in animals. Understanding the roles of deubiquitinases and proteasomes in the regulation of OATs, a novel focus in drug transport field, will have significant impact on the future design of strategies aimed at maximizing therapeutic efficacy and minimizing toxicity, and will permit insight into the molecular, cellular, and clinical bases of renal, hepatic, neurological and fetal toxicity and disease.